At present, gene therapy is performed as one method for treating cancers. However, since a gene is introduced into diseased tissue or the like with a non-replication competent virus vector in gene therapy, the gene can be applied to only those regions around target cells taking into consideration the safety of the human body. Also, in the gene therapy currently practiced, satisfactory therapeutic effect cannot be achieved because of low efficiency in gene transfer.
It is known that telomerase activity is often enhanced in malignantly transformed cells or immortalized cell strains, whereas telomerase activity is hardly detected in normal somatic cells excluding such as germ line cells, blood lineage cells and epithelial stem cells.
Under circumstances, it is a major object of the present invention to let a virus grow in tumor cells by utilizing the telomerase activated therein to thereby bring death to the tumor cells efficiently.